This invention relates to low pressure mercury vapor discharge lamps having high electrical and/or thermal loading, and preferably to fluorescent lamps containing an amalgam. The vapor pressure of such lamps is determined by the characteristic of the amalgam to have a lower mercury vapor pressure than free mercury at the same temperature.
As is well known, (i) the composition of the amalgam both in relation to the selection of the amalgam-forming metal and to its quantitative proportion in the alloy, and (ii) also the location of the amalgam-forming metal or amalgam, respectively, is of importance for the amalgam function within the lamp in order to adapt the lamp to a predetermined use or to obtain a lamp for use in a wide variety of applications. The temperature in a given location within the lamp is determinative of the possibility of locating an amalgam therein.
Many different locations and modes of application of the amalgam are known, such as applying the amalgam at a predetermined distance from the electrodes, preferably to the inner wall surface of the discharge tube in the form of a strip, a film, or a pellet. The amalgam then was secured in the predetermined location by rolling, or it was placed on a metal foil coated with a plastic adhesive and the metal foil was secured in the location, or, after heating to softening temperature, it was thrust by pressure against the bulb wall for adhesion (see U.S. Pat. No. 3,152,278; U.S. Pat. No. 3,160,778; U.S. Pat. No. 3,351,797 and German Patent DT-PS No. 1 149 818). It is also known to position the amalgam in a sieve-like container (see British Pat. No. 1,097,090) or to place around the lamp stem a mesh of nickel saturated with indium as the amalgam-forming metal (see Ill. Eng. 60 (1965), No. 9, page 534) or, to apply the amalgam-forming metal as a fine dispersion by spraying on the flare of at least one electrode stem (see U.S. Pat. No. 3,548,241).
It is an object of the present invention to provide a lamp in which the amalgam or the amalgam-forming metal has been secured in an improved manner.